shut off tank when on vacation

My preference is to shut off a water heater and water when going away for a couple of days or more. Someone mentioned the cooling water would subject you to bacteria on your return. Would not turning the WH back on (say, set at 140 with a tempering valve) protect and "clean" your water in a few hours or overnight with that heat?

The danger zone for legionella is storage temps between about 85F and 115F. Below 85F it just doesn't grow very quickly, nor above 115F. While it takes 140F to outright kill an established colony (and it takes days not hours at a mere 140F) it's very hard for a colony to get established even at 120F storage temps.

So, when you go away for several days the temps will fall through the danger zone to some lower temp- usually below the zone except in the middle of summer in homes with a lot of solar gain and the air conditioning off. If the heater is located in a below-grade NJ basement it's unlikely to stagnate at 85F under any realistic weather & solar gain scenario.

Seriously- every time you draw hot water water abandoned in the plumbing goes through the same cooling through the danger zone situation, and far more often than the turned-off tank does. In the rare instances where the distribution plumbing ends up being contaminated with established legionella colonies, the sterilization protocol is to purge with 160F water for something like a couple of hours.

I have a seasonal cottage that's unoccupied 90% of the year and the standard HWH is on "pilot" during that time. Mine is close to a worst-case scenario in that I'm on untreated well water from a 25-foot-deep well and I've had no problems with sickness, the runs (can't spell diarrhea), or any bad smells.

A bonus: I was amazed to find that the water in my standard 40G gas water heater, with no extra insulation and in an uninsulated garage, stays hot enough with that little pilot flame to take a hot shower after it's been shut down for weeks. And I've always been told a standing pilot is a waste of energy ;-)

And a standing pilot IS a waste of energy. It's enough heat to pretty much balance the standby losses, but those standby losses are real. Most standing pilots on water tanks consume on the order of ~500,000 BTU per month give or take- you're talking 5-6 therms or 6+ gallons of propane per month for the convenience of having the water hot enough to use the instant you arrive.

Recovery times from room temp is pretty reasonable for gas or propane fired tanks, so yeah, it really is kind a waste in a seasonal cottage only occupied 10% of the time.

I could never recommend allowing a water heater to drop below the 120 deg.F. mark for any period of time. If you are gone for just a few days, what is the harm in leaving the tank stay as it is. It is unknown at any time how much legionella bacteria may exist in your public water system at any time. Typically there are low amounts of microrganisms depending on what type of chemicals are being used for water treatment and they have no affect on us because of the low concentration. But don't try to sell yourself into an idea that promotes a lack of safety, err on the side of caution.
Some may say that they have never gotten sick from their hot water, but may have and not realized it. The symptoms are the same as the flu and may take just as long after exposure to show the symptoms. Children and the elderly are especially susceptible to the health risks when exposed. Rarely is ingestion of contaminated water a cause, unless aspirated. It is when taking a shower that it is inhaled with the vapors and settles in the lungs.
The ideas that water sits in the pipes anyways and that temperatures drop in the tank when cold water is used are geared towards ignoring the core issue of safety with your water system.
Just flush the pipes when you walk in the door and keep your tank at the normal operating temperature and you won't have to worry about Pasteurizing your tank or chlorinating the piping.

I'm sure there have been studies. Anything related to conserving resources and being "green" has been studied to death and something that could also affect health I would think would be near the top of the list.

We all need to be worried, Go to the doctor and get more shots and pills.

Then see what kills you first.

Some Old folks like them Microorgasims.

Have Fun.

Click to expand...

Maybe for you, but not for the 29 old folks who were sickened and the 6 old folks who died recently at the VA hospital in Pittsburgh. Just Google how many people were sick and how many died in 2012. Thousands in just the US, Canada and England. Joke about it now..."It won't happen to me" always happens to somebody. It doesn't take a rocket scientist to realize it, either.

Most of the planets inhabitants would be long gone if the water wasn't "just right".

How about thinking about the billions of people that don't have a problem rather than a few who likely have a myriad of physical problems.

Humans didn't become rulers of this planet by following the "Goldilocks" plan of survival.

Click to expand...

Okay, common sense has just officially left this thread. What you just said was so freakin' stupid I'm surprised that natural selection hasn't already eliminated you and your microorganisms from the planet. You must have forgotten about the discovery of antibiotics, the invention of optics to help your failing eyesight and the surgeries that may have saved your life or somebody you love. Advancements in science have benefited the human race and ALLOWED us to live longer when the natural world would haveal ready killed us. You also have reaped the benefits of these advancements of electricity and gas for heating and cooling and automobiles to save burning houses and lives, but you are too stupid or ignorant toadmit that without them you would have never lived this long. Good! go off into a cave and see how long you last. Report back in a year with us on your Internet machine if you have the balls to stand by your words and convictions. Dummy.

Okay, common sense has just officially left this thread. What you just said was so freakin' stupid I'm surprised that natural selection hasn't already eliminated you and your microorganisms from the planet. You must have forgotten about the discovery of antibiotics, the invention of optics to help your failing eyesight and the surgeries that may have saved your life or somebody you love. Advancements in science have benefited the human race and ALLOWED us to live longer when the natural world would haveal ready killed us. You also have reaped the benefits of these advancements of electricity and gas for heating and cooling and automobiles to save burning houses and lives, but you are too stupid or ignorant toadmit that without them you would have never lived this long. Good! go off into a cave and see how long you last. Report back in a year with us on your Internet machine if you have the balls to stand by your words and convictions. Dummy.

Click to expand...

You're off to a great start on here. I don't think you'll be welcome long.

I totally disagree with your extreme view. Life is full of risks and "that which doesn't kill us makes us stronger". I don't care to live in a rubber-padded antiseptic world with "big brother" watching over me. I'm not going to get sick and die from organisms growing in my closed water system, and neither are you. Let's focus our talents and attention on things that matter.

I could never recommend allowing a water heater to drop below the 120 deg.F. mark for any period of time. If you are gone for just a few days, what is the harm in leaving the tank stay as it is. It is unknown at any time how much legionella bacteria may exist in your public water system at any time. Typically there are low amounts of microrganisms depending on what type of chemicals are being used for water treatment and they have no affect on us because of the low concentration. But don't try to sell yourself into an idea that promotes a lack of safety, err on the side of caution.
Some may say that they have never gotten sick from their hot water, but may have and not realized it. The symptoms are the same as the flu and may take just as long after exposure to show the symptoms. Children and the elderly are especially susceptible to the health risks when exposed. Rarely is ingestion of contaminated water a cause, unless aspirated. It is when taking a shower that it is inhaled with the vapors and settles in the lungs.
The ideas that water sits in the pipes anyways and that temperatures drop in the tank when cold water is used are geared towards ignoring the core issue of safety with your water system.
Just flush the pipes when you walk in the door and keep your tank at the normal operating temperature and you won't have to worry about Pasteurizing your tank or chlorinating the piping.

Click to expand...

So, you must keep heaters on the distribution plumbing to make sure the gallons of water in the hot water distribution never drops below 120F then?

When turning off the hot water heater the time window of growth risk is pretty fleeting- once the temp of the tank drops to 85F the legionalla growth rates are about the same as at 120F. Water stored at room temp does not promote the growth of legionella. Do you purge the cold water distribution plumbing too? How about the 70F water coming in from the street all summer in warmer climates?

Even at the prime growth temps it takes weeks or months, not hours or days for a colony to become established. Keeping long term storage temp at 110F-115F to save energy carries some risk. Letting the tank temp fall through those temps down to sub-85F over the course of a day or three does not. If you normally maintain the storage temp at 140F there are no live legionella bacteria in the tank to even START a legionella colony. There can be some live 'uns in the tank if you only keep it at 120F, but nothing is going to suddenly take off in the few dozen hours it takes to drop from 120F to under 85F. The highest growth rate zone is between 90F-105F- above 110F or below 85F it can grow, but it's pretty slow. At 75F or 120F it won't die, but it can't reproduce at more than self-replacement rates. And at 135F-140F colonies are guaranteed to die off-eventually. (It takes higher temps to kill it instantly.)

The original post asked if there was any risks to just turning off a 140F tank whenever the place was going to be unoccupied for more than a couple of days, and the answer is there is none- it starts out sterile, and even if you drew in some live legionella just before turning it off, it doesn't stagnate in the high-growth temperature zone long enough to matter.

Maybe for you, but not for the 29 old folks who were sickened and the 6 old folks who died recently at the VA hospital in Pittsburgh. Just Google how many people were sick and how many died in 2012. Thousands in just the US, Canada and England. Joke about it now..."It won't happen to me" always happens to somebody. It doesn't take a rocket scientist to realize it, either.

None of you really have any idea what you're talking about. Seriously. When somebody asks for advice about safety in a water heater, you reply with cute quips and sassy witticisms but actually contribute nothing to the OP. You are to afraid to accept an opinion other than your own, and you see your own opinion as a fact. The fear of being welcome or not doesn't change anything about what I said, and you can continue to chirp about things you really don't understand and get applause from your buddies, but you still failed the original posters test of answering the question with good sense and good information. You may have impressed yourself with your responses and attitudes, but to me and the other registered plumbers who actually feel responsible for protecting the public from the ignorance of people like you...you will always appear to be just stupid. Until next time...stay healthy!

So, you must keep heaters on the distribution plumbing to make sure the gallons of water in the hot water distribution never drops below 120F then?

When turning off the hot water heater the time window of growth risk is pretty fleeting- once the temp of the tank drops to 85F the legionalla growth rates are about the same as at 120F. Water stored at room temp does not promote the growth of legionella. Do you purge the cold water distribution plumbing too? How about the 70F water coming in from the street all summer in warmer climates?

Even at the prime growth temps it takes weeks or months, not hours or days for a colony to become established. Keeping long term storage temp at 110F-115F to save energy carries some risk. Letting the tank temp fall through those temps down to sub-85F over the course of a day or three does not. If you normally maintain the storage temp at 140F there are no live legionella bacteria in the tank to even START a legionella colony. There can be some live 'uns in the tank if you only keep it at 120F, but nothing is going to suddenly take off in the few dozen hours it takes to drop from 120F to under 85F. The highest growth rate zone is between 90F-105F- above 110F or below 85F it can grow, but it's pretty slow. At 75F or 120F it won't die, but it can't reproduce at more than self-replacement rates. And at 135F-140F colonies are guaranteed to die off-eventually. (It takes higher temps to kill it instantly.)

The original post asked if there was any risks to just turning off a 140F tank whenever the place was going to be unoccupied for more than a couple of days, and the answer is there is none- it starts out sterile, and even if you drew in some live legionella just before turning it off, it doesn't stagnate in the high-growth temperature zone long enough to matter.

Click to expand...

You need to educate yourself a little more than what you get off of the internet. You are trying to reason with too little understanding of the whole subject matter. You come off as sounding kinda smart, I'll give you that, but that's just sounding smart...not actually BEING smart. Wikipedia isn't a substitute for years of education and experience. Keep up the show for the others that are entertained here, but your circle of failed logic looks like the juggling act of a circus clown.

Caduceus-
So far everyone else here is stupid, a dummy, or a clown but if you can't back up your opinions--no matter how heartfelt or evangelically expressed--they'll never become facts.

Your fervor + your location & icon might lead one to assume you're personally involved in the Pittsburgh VA hospital legionnaire outbreaks. What's the problem with THEIR system that isn't affecting the rest of the city? Or is it just another case of people going to the hospital and coming out sicker than when they arrived?